(1) Field of the Invention
The present invention relates to microcapsules filled with N,N-diethyl m-toluamide (hereinafter referred to as "diethyltoluamide") of a formula: ##STR2##
More precisely, it relates to microcapsules filled with diethyltoluamide which is effective as a repellent to insanitary vermine of a broad range, such as mosquitos, gnats, lies, horseflies, cockroaches, fleas, tsutsugamushi mites and acarids, and the microcapsules are improved to be free from the defect in use of the original diethyltoluamide.
(2) Description of the Prior Art
Insects of 1,800,000 kinds or more are known, and these include a group or so-called insanitary insects (vermin) which have directly or indirectly some bad influences on a human life.
Insanitary vermin typically include the following kinds:
Mosquitos which bite human and animal bodies to cause extreme itch, erubescence and swelling on the bitten skins and which carry various infectious diseases of Japanese B encephalitis, dengue, yellow fever, malaria, filariasis or the like; gnats, horseflies and rice-bran mosquitos whose female imagoes extremely bite human and animal bodies to often carry infectious diseases; cockroaches which carry infectious disease bacteria such as cholera bacillus, typhoid bacillus or dysentery bacillus as well as other pathogenic bacteria such as tubercle bacillus; tsutsugamushi mites to cause tsutsugamushi disease; and acarids which extremely bite human and animal bodies to such blood therefrom and which cause allergy disease. In addition, insanitary vermin further include clothes vermin such as clothes moths or webbing clothes moths, as well as fleas, flies and ants.
It is well known that diethyltoluamide is effective as a chemical agent for repelling the said insanitary vermin, but unfortunately, diethyltoluamide is defective in that this is poor in a long-time durability. Under the present situation, therefore, it is earnesly desired to overcome the said defect and to prolong the durability of the pharmaceutical potency of diethyltoluamide as long as possible. For the purpose, some means have heretofore been investigated, all of which, however, were insufficient.
As a method of killing insanitary vermin, spraying of an insecticide as well as use of an aerosol or fumigant containing an insecticide as an active ingredient is generally carried out. However, use of an insecticide of a high concentration is presumed to have some bad influence on human bodies, and in addition, it has various problems that vermin would again come to the treated region when the effective potency of the insecticide has vanished with the lapse of a certain period of time after the insecticide was applied to the region, vermin would have a chemical resistance to the insecticide after repeated and continuous application of the same insecticide to the same place so that the insecticide becomes ineffective to the resulting chemical-resistant vermin, and the died vermin are required to be taken away.
As one method for evading the said problems, an insanitary vermin repellent has heretofore been studied, and a lot of substances effective as a vermin-repellent have been found which include, for example, diethyltoluamide, N-butylacetanilide, 2-ethyl-1,3-hexanediol, 2-butyl-2-ethyl-1,3-propanediol and propyl mandelate. Among these repllents, diethyltoluamide is considered to be the most ideal repellent at the present time because of the reasons that the scope of the objects to be repelled thereby is broad, the safety is high, this hardly drops from clothes after applied thereto, this is excellent in the proofness to sweat and water and this has no odor offensive to human.
As means of using diethyltoluamide, there are known the following ways: Briefly, this is used in the form of a preparation of an aerosol, cream or lotion as a vermin-repellent for application to human bodies; diethyltoluamide of its original form is dissolved in a pertinent solvent or latex and coated, penetrated or incorporated into pile yarns, base clothes or packing materials of carpets so as to repell acarids or other vermin therefrom; or diethyltoluamide is penetrated into parts of the ceiling, side walls and drawers of clothes cabinets or parts of plate-racks to obtain vermin-repellent furnitures and plate-racks.
However, there are various problems in use of diethyltoluamide and therefore, the utilization thereof is limited to a defined range. A repellent is desired to have a vapour pressure of some degree so that the active ingredient may effectively vapourize, but if the vapourization is too extreme, the repellent effective time would be shortened. Under the circumstances, therefore, some particular treatment is required for vermin-repellent carpets and vermin-repellent furnitures which need the vermin-repellent effect for a long period of many years. The vapourization and reduction of the active ingredient is often influenced by the environmental light and temperature, and therefore the protection of the active ingredient is also required. Regarding vermin-repellents for application to human bodies, almost all of them are in the form of an aerosol type because the use is easy and the stability of the active ingredient and the preparation itself is good. However, such aerosol type vermin-repellents have defects that the active ingredient diffuses in air, and the active ingredient is absorbed into a body too rapidly through the skin so that the repellent effect could not last long on the skin. Moreover, a solvent such as an alcohol is added to the repellent preparation since diethyltoluamide is hardly soluble in water, and therefore, the preparation is stimulative to a wounded skin and it is flammable.
In order to overcome these defects of the diethyltoluamide-containing preparation, other means have been considered where diethyltoluamide is blended with an urethane resin or a cellulose derivative and coated on the wall of furnitures to form a hardened film thereon so as to prolong the effective life of diethyltoluamide coated, or a sweat-inhibiting substance is used together with diethyltoluamide for application to human bodies so as to reduce the endermic absorption of of diethyltoluamide and to prolong the effective life thereof coated on the skin. However, both of the said means were insufficient since the control of the vapourization speed of diethyltoluamide on the skin coated is difficult.